Dual frequency comb spectroscopy in the molecular fingerprint region

TL;DR

This paper introduces a robust method for generating super-octave optical frequency combs in the molecular fingerprint region, enabling high-precision dual-comb spectroscopy for chemical sensing and imaging.

Contribution

The authors develop a simple intra-pulse difference frequency generation technique in gallium phosphide to produce broad frequency combs in the fingerprint region, advancing molecular spectroscopy capabilities.

Findings

Successful generation of super-octave frequency combs in the 6.5-20 μm range.

High-precision dual-comb spectroscopy demonstrated on methanol and ethanol vapors.

Potential applications in molecular sensing and nanoscopic imaging.

Abstract

Spectroscopy in the molecular fingerprint spectral region (6.5-20 $\mu$m) yields critical information on material structure for physical, chemical and biological sciences. Despite decades of interest and effort, this portion of the electromagnetic spectrum remains challenging to cover with conventional laser technologies. In this report, we present a simple and robust method for generating super-octave, optical frequency combs in the fingerprint region through intra-pulse difference frequency generation in an orientation-patterned gallium phosphide crystal. We demonstrate the utility of this unique coherent light source for high-precision, dual-comb spectroscopy in methanol and ethanol vapor. These results highlight the potential of laser frequency combs for a wide range of molecular sensing applications, from basic molecular spectroscopy to nanoscopic imaging.